The present invention relates to a component mounting device, and more particularly, to a device for automatically mounting electronic components, such as semiconductor devices, on a printed circuit board.
A component mounting device, called a mounter, automatically mounts electronic components, such as semiconductor devices, diodes, capacitors, or resistors, on a printed circuit board. The mounting device includes a board supporting stage having guide rails for guiding the printed circuit board to a predetermined position, a component stage that supports various electronic components to be mounted on the printed circuit board, and a mounting head that moves horizontally to pick up the electronic components from the component stage and mount them at predetermined locations on the printed circuit board.
The mounting head includes several suction nozzles, or suction bits, for picking up the electronic components using vacuum suction. The suction nozzles move up and down with respect to the board supporting stage and the component stage.
The mounting head also includes a position determination chuck, that is, a mechanism that determines the position of the picked-up electronic component held by the suction bit. The position determination chuck assures that the electronic component is positioned at a predetermined position with respect to the suction bit, or in other words, that the suction bit has a proper hold on the electronic component. When the electronic component is not positioned at the predetermined position, the position determination chuck corrects the electronic component's position using a position determination finger.
For electronic components that do not require high precision mounting, the mounting head mounts the electronic components after the position determination chuck determines the position of the electronic components as described above.
Some types of electronic components, however, require high precision mounting. For high precision mounting, the component mounting device uses optical detection to determine whether the picked-up electronic component is positioned at the predetermined position with respect to the suction bit. Typically, the mounting device uses a camera to determine whether the center of the electronic component aligns with the center of the suction bit, and the degree of rotation of the electronic component with respect to the suction bit.
The component mounting device processes the image data received by the camera to detect the amount of deviation of the picked-up electronic component in a horizontal direction with respect to a reference position of the suction bit. Then, as the mounting head carries the picked-up electronic component to a mounting position on the printed circuit board, the mounting head corrects the electronic component's deviation so as to accurately mount the electronic component on the printed circuit board. Position correction using image processing takes more time than other types of position correction, but provides a more accurate position determination.
The camera captures the image of the electronic component using one of several capture techniques: the backlight or transmission type of capture, or the front-light or reflection type of capture. In the backlight type, a light source is located opposite the camera so that the illumination transmits through the electronic component. In the front-light type, on the other hand, the light source is located on the side of the camera so that the illumination reflects off of the electronic component.
Conventionally, the mounting device positions the camera at a bottom portion of the mounting device, and positions the light source in the mounting head. By this arrangement, the camera captures the image of the component through the backlight type of capture. After the suction bit picks up the electronic component, the camera captures the image of the component to determine whether the electronic component is located at the predetermined position with respect to the suction bit.
When the mounting head contains the light source, one of the mounting heads typically acts as a head for image processing only. This reduces the number of suction bits that can be installed in the mounting heads and thereby lowers the component mounting speed and mounting efficiency of the mounting device.
Typically, the mounting device locates the camera at the bottom portion of the mounting device, between the board support stage and the component stage. The camera captures the image of the electronic component while the mounting head carries the electronic component from the component stage to the board support stage. To accommodate the camera being installed between the board support stage and the component stage, however, the component mounting device must be made larger in the horizontal direction. This decreases the mounting speed because the electronic component needs to be carried over a longer distance.
When a position determination chuck is installed at the suction bit and the camera is of the front-light type (reflection type), the camera captures not only an image of the picked-up electronic component, but also the hook, or finger, portion of the position determination chuck. As a result, the mounting device cannot accurately process the captured image.
Moreover, the components, whose picked-up positions are accurately detected by image processing, occupy only a small portion of the electronic components to be mounted on the printed circuit board. Accordingly, the position determination process cannot be accurately performed with respect to a majority of the electronic components.